1. Field of Invention
The present invention relates to a thin film transistor liquid crystal display (TFT-LCD). More particularly, the present invention relates to a method of controlling the capacitance of a TFT-LCD storage capacitor.
2. Description of the Related Art
Liquid crystal display (LCD) has many advantages over other conventional types of displays including high display quality, small volume occupation, lightweight, low voltage driven and low power consumption. Hence, LCDs are widely used in small portable televisions, mobile telephones, video recording units, notebook computers, desktop monitors, projector televisions and so on. Therefore, LCD has gradually replaced the conventional cathode ray tube (CRT) as a mainstream display unit.
The gate dielectric layer of the thin film transistor in the TFT-LCD is generally a silicon nitride layer. When a source/drain stacked layer in a bottom gate structure or a gate in a top gate structure is formed on the gate dielectric layer, a short period of over-etching is performed to make sure that no residues are left on the gate dielectric layer. Since the area of the transparent substrate is very large, the thickness uniformity of the gate dielectric layer after over-etching on the entire transparent substrate is not good. Thus, the thickness uniformity of the storage capacitor dielectric layer in each pixel is also affected.
The storage electricity of the storage capacitor is used to compensate for the leakage current of the pixel electrode, and the pixel electrode voltage can therefore be maintained at a stable level to stabilize the arrangement of liquid crystal molecules to stabilize the display of LCD. If the capacitances of the capacitors on the transparent substrate are varied, the charging or discharging rates are also varied. Therefore, the TFT dimensions cannot be designed according to the ideal condition that each storage capacitor has the same capacitance. To insure that a storage capacitor with less sufficient capacitance can normally charge and discharge in a regular time period, the TFT dimensions have to be designed large enough to enable the poorest storage capacitor to function normally. Therefore, the stability of the TFT-LCD display can be maintained. However, the aperture ratio of each pixel in TFT-LCD is decreased.